Characterization of T-shaped terminal impedances of differential short stubs in advanced CMOS technology

For short stubs in advanced CMOS technology, small terminal impedances are achieved by employing differential transmission lines and making virtual ground. However, no quantitative evaluation method for the terminal impedance of a differential short stub has been reported. To characterize the terminal impedance accurately, we propose the use of a T-shaped terminal impedance model of differential short stubs, where terminal impedance is evaluated by applying differential-mode and common-mode signals. In this paper, we describe the T-shaped terminal impedance model and the characterization procedure for terminal impedance. From measurement data, it is shown that the T-shaped terminal impedance of differential short stubs is successfully evaluated.